Phosphorus speciation in mature wheat and canola plants as affected by phosphorus supply

Background and aims

As plants approach maturity and start to senesce, the primary sink for phosphorus (P) is the seed but it is unclear how plant P status affects the resulting P concentration and speciation in the seed and remaining plant parts of the residues. This study was established to measure how P speciation in different parts of wheat and canola is affected by plant P status.

Methods

Wheat and canola grown in the glasshouse were supplied three different P rates (5, 30 and 60 kg P ha^?1 equivalent). At physiological maturity, plants were harvested and P speciation was determined for all plant parts (root, stem, leaf, chaff/pod and seed) and rates of P application, using solution ³¹P nuclear magnetic resonance (NMR) spectroscopy.

Results

Phytate was the dominant form of P in seed whereas orthophosphate was the dominant form of P in other plant parts. The distribution of P species varied with P status for canola but not for wheat. The phytate content of wheat chaff increased from 10 to 45 % of total P as the P rate increased. Canola pods did not show a similar trend, with most P present as orthophosphate.

Conclusions

Although minor differences were observed in P speciation across the three P application rates and plant parts, the effect of this on P cycling from residues into soil is likely to be relatively minor in comparison to the overall contribution of these residues to soil P pools. This glasshouse experiment shows the dominant P form in crop residues that is returned to soil after harvest is orthophosphate, regardless of plant P status.     

Integrated effects of organic,inorganic and biological amendments on methane emission,soil quality and rice productivity in irrigated paddy ecosystem of Bangladesh: field study of two consecutive rice growing seasons

Aims

Effects of different soil amendments were investigated on methane (CH₄) emission, soil quality parameters and rice productivity in irrigated paddy field of Bangladesh.

Methods

The experiment was laid out in a randomized complete block design with five treatments and three replications. The experimental treatments were urea (220 kg ha^?1) + rice straw compost (2 t ha^?1) as a control, urea (170 kg ha^?1) + rice straw compost (2 t ha^?1) + silicate fertilizer, urea (170 kg ha^?1) + sesbania biomass (2 t ha^?1 ) + silicate fertilizer, urea (170 kg ha^?1) + azolla biomass (2 t ha^?1) + cyanobacterial mixture 15 kg ha^?1 silicate fertilizer, urea (170 kg ha^?1) + cattle manure compost (2 t ha^?1) + silicate fertilizer.

Results

The average of two growing seasons CH₄ flux 132 kg ha^?1 was recorded from the conventional urea (220 kg ha^?1) with rice straw compost incorporated field plot followed by 126.7 (4 % reduction), 130.7 (1.5 % reduction), 116 (12 % reduction) and 126 (5 % reduction) kg CH₄ flux ha^?1 respectively, with rice straw compost, sesbania biomass, azolla anabaena and cattle manure compost in combination urea and silicate fertilizer applied plots. Rice grain yield was increased by 15 % and 10 % over the control (4.95 Mg ha^?1) with silicate plus composted cattle manure and silicate plus azolla anabaena, respectively. Soil quality parameters such as soil organic carbon, total nitrogen, microbial biomass carbon, soil redox status and cations exchange capacity were improved with the added organic materials and azolla biofertilizer amendments with silicate slag and optimum urea application (170 kg ha^?1) in paddy field.

Conclusion

Integrated application of silicate fertilizer, well composted organic manures and azolla biofertilizer could be an effective strategy to minimize the use of conventional urea fertilizer, reducing CH₄ emissions, improving soil quality parameters and increasing rice productivity in subtropical countries like Bangladesh.     

Potassium release characteristics, potassium balance, and fingermillet (Eleusine coracana G.) yield sustainability in a 27- year long experiment on an Alfisol in the semi-arid tropical India

Aims

In Alfisols, potassium (K) deficiency limits productivity, as these soils are poor in K-bearing minerals such as mica. As nutrient management practices greatly influence K nutrition of crops especially in the longer term, we evaluated the effects of 27 (1978–2004) years of cropping fingermillet (Eleusine coracana G.) under different manure and mineral fertilizer treatments on K release, balance and yield sustainability on K deficient Alfisols in the semi-arid tropical region of southern India.

Methods

Fingermillet (variety: PR-202) was grown each year under rainfed conditions with 5 different nutrient management treatments: control (no amendment), 10 Mg ha^?1 farm yard manure (FYM), 10 Mg ha^?1 FYM +50 % NPK, 10 Mg ha^?1 FYM +100 % NPK and 100 % NPK. Potassium release characteristics in the soil profile were determined using 1 N boiling HNO₃ (strong extracting solution), 0.01 M HCl (medium extracting solution) and 0.01 M CaCl₂ (mild extracting solution).

Results

Continuous cropping of Alfisols for 27 years resulted in a decrease in K supplying capacity due to soil K depletion through crop K uptake. In soils without K addition, inherent soil supply could not meet the K requirement of fingermillet; thus, a negative K balance following 27 years of cropping affected K nutrition of the crop in all the treatments. As a result, the highest sustainable yield index (SYI) was observed using an integrated nutrient supply (combined application of nutrients from organic and inorganic sources), and the lowest index was obtained without K additions.

Conclusion

For balanced nutrient management in cereal production systems, K nutrition needs urgent attention in the K deficient Alfisol region of southern India. Addition of any amount of organic manures available at field level offers an alternative strategy for maintaining soil K fertility to improve and sustain crop productivity.     

Stable carbon and nitrogen isotope ratios of Eucalyptus and Acacia species along a seasonal rainfall gradient in Western Australia

Key message

Eucalyptus and Acacia species were surprisingly similar with respect to variations in δ ¹³ C, δ ¹⁵ N. Both genera respond with speciation and associated changes in leaf structure to drought.

Abstract

Stable carbon and nitrogen isotope ratios (δ¹³C and δ¹⁵N) in leaves of eucalypts (Corymbia and Eucalyptus) and Acacia (and some additional Fabaceae) species were investigated together with specific leaf area (SLA), leaf nitrogen (N) and leaf phosphorous (P) concentration along a north–south transect through Western Australia covering winter- and summer-dominated rainfall between 100 and 1,200 mm annually. We investigated 62 eucalypts and 78 woody Fabaceae species, mainly of the genus Acacia. Leaf δ¹³C values of Eucalyptus and Acacia species generally increased linearly with latitude from ?29.5 ± 1.3 ‰ in the summer-dominated rainfall zone (15°S–18°S) to about ?25.7 ± 1.1 ‰ in the winter-dominated rainfall zone (29°S–31°S). δ¹⁵N increased initially with southern latitudes (0.5 ± 1.6 ‰ at 15°S; 5.8 ± 3.3 ‰ at 24–29°S) but decreased again further South (4.6 ± 3.5 ‰ at 31°S). The variation in δ¹³C and δ¹⁵N was probably due to speciation of Eucalyptus and Acacia into very local populations. There were no species that were distributed over the whole sampling area. The variation in leaf traits was larger between species than within species. Average nitrogen concentrations were 11.9 ± 1.05 mg g^?1 in Eucalyptus, and were 18.7 ± 4.1 mg g^?1 in Acacia. Even though the average nitrogen concentration was higher in Acacia than Eucalyptus, δ¹⁵N gave no clear indication for N₂ fixation in Acacia. In a multiple regression, latitude (as a surrogate for rainfall seasonality), mean rainfall, leaf nitrogen concentration, specific leaf area and nitrogen fixation were significant and explained 69 % of the variation of δ¹³C, but only 36 % of the variation of δ¹⁵N. Higher nitrogen and phosphorus concentration could give Acacia an advantage over Eucalyptus in arid regions of undefined rainfall seasonality.     

Fertilization enhancing carbon sequestration as carbonate in arid cropland: assessments of long-term experiments in northern China

Aims

Soil inorganic carbon (SIC), primarily calcium carbonate, is a major reservoir of carbon in arid lands. This study was designed to test the hypothesis that carbonate might be enhanced in arid cropland, in association with soil fertility improvement via organic amendments.

Methods

We obtained two sets (65 each) of archived soil samples collected in the early and late 2000’s from three long-term experiment sites under wheat-corn cropping with various fertilization treatments in northern China. Soil organic (SOC), SIC and their Stable ¹³C compositions were determined over the range 0–100 cm.

Results

All sites showed an overall increase of SIC content in soil profiles over time. Particularly, fertilizations led to large SIC accumulation with a range of 101–202 g C m^?2 y^?1 in the 0–100 cm. Accumulation of pedogenic carbonate under fertilization varied from 60 to 179 g C m^?2 y^?1 in the 0–100 cm. Organic amendments significantly enhanced carbonate accumulation, in particular in the subsoil.

Conclusions

More carbon was sequestrated in the form of carbonate than as SOC in the arid cropland in northern China. Increasing SOC stock through long-term straw incorporation and manure application in the arid and semi-arid regions also enhanced carbonate accumulation in soil profiles.     

Effect of long-term tillage and mineral phosphorus fertilization on arbuscular mycorrhizal fungi in a humid continental zone of Eastern Canada

Aims

Evidence shows that tillage modifies soil properties, especially phosphorus (P) dynamics. Our objective was to disentangle long-term effects of P-fertilization and tillage on arbuscular mycorrhizal fungal (AMF) proliferation and community structure.

Methods

Changes in the community structure of AMF and in the density of their hyphae and spores induced by moldboard plow (MP) or no till (NT), and fertilization with 0, 17.5, or 35 kg?P?ha^?1 were sought in the 0–15 cm and 15–30 cm soil layers after soybean harvest, at a long-term (17 years) experimental site in a humid continental zone of eastern Canada. The relationships among AMF, soil and plant attributes were examined.

Results

The 0–15 cm and 15–30 cm soil layers had different properties under NT, but were similar under MP, after 17 years, and MP increased soil available P levels. Phosphorus fertilization increased P levels in soil and in soybean. Treatment effects on AMF spore and hyphal density at 0–15 cm were greater than that at 15–30 cm, whereas effects on AMF community structure did not change with soil depths. At 0–15 cm, P-fertilization increased AMF spore density and reduced AMF hyphal density, and MP reduced AMF spore density. A total of eight AMF phylotypes were detected. Phosphorus fertilization reduced AMF phylotype richness and Shannon diversity index. Soil P availability increased under MP and hence the influence of P-fertilization treatments on the frequency of AMF phylotype detection varied with tillage system; it declined with P-fertilization under MP, but increased under NT.

Conclusions

Phosphorus fertilization shifts resource partitioning in AMF propagules rather than in their hyphae, and degrades the genetic diversity of AMF in soil; tillage increases soil P availability and hence aggravates the impact of P-fertilization.     

The phosphorus concentration of common rocks—a potential driver of ecosystem P status

Background

Soil phosphorus (P) availability can be an important regulator of ecosystem processes. Changes in P availability over time have long been studied, but the P concentration of soil parent materials—which determines ecosystem P concentration at the onset of soil formation—have never been systematically explored. Here we ask two questions: 1) how does P concentration vary among soil parent materials? and 2) under what range of conditions do those differences influence soil P concentration?

Methods

We used the Earthchem webportal to compile the P concentration of 263,539 rocks. We then gathered data from 62 sites (MAT ranging from 200–5,000 mm?yr^-1 and soil age from 0.3–4,100 ky) and assessed the correlation between rock and soil P concentration.

Results

We found a 30 fold difference in median P concentration among rock types, ranging from 120 ppm (several ultramafic rocks) to >3,000 ppm (several alkali basalts). Median P was significantly lower in common silica-rich rocks (e.g. granite - 436 ppm) and higher in common iron-rich rocks (e.g. andesite - 1,000 ppm). In sedimentary rocks, which make up 70 % of the ice-free land surface, median P was highest in mudstone (1,135 ppm) and decreased with increasing grainsize (siltstone-698 ppm, sandstone-500 ppm). Where soil P and parent material P were measured in the same site, parent material P explained 42 % of the variance in total soil P (n?=?62), and explanatory power was higher for sites with similar climate.

Conclusion

The variation in P concentration among common rock types is on a comparable scale to the changes in total P, and several P pools, over long-term soil development. Quantifying these differences may be an important step towards characterizing regional and global variation in soil and ecosystem P status.     

A resin buffered method for controlling metal speciation in nutrient solutions for plant toxicity tests

Aims

Root elongation tests are sensitive bioassays for testing metal toxicity in nutrient solutions. The metal speciation and, hence, metal exposure conditions are little controlled in the traditional set-up. A resin buffered solution system was developed to overcome this issue.

Methods

Barley (Hordeum vulgare L.) root elongation was tested in aerated 140 mL solution batch systems supplied with 3.3 g Dowex resin for two plants. Copper toxicity was measured in presence or absence of the resin (+R/?R) and in presence or absence of a metal complexing ligand (+NTA; nitrilotriacetic acid/?NTA). In addition, the toxicity in the traditional set without resin and with daily solution replacement was included as a reference.

Results

Metal desorption from the resin is fast in these systems (k?=?0.82 h^?1). Total dissolved Cu roughly halved during 4 days in ?R/?NTA systems due to uptake, while it increased by 30 % in the +R/?NTA, probably due to complexation reactions by root-derived molecules. The toxicity (50 % reduction in root length, EC50) of the initial free Cu²⁺ was equal in all resin or chelate buffered systems and in the solutions with daily replacement, whereas this threshold was significantly larger in the ?R/?NTA due to Cu²⁺ uptake and complexation reactions.

Conclusion

The resin method is a convenient system for high throughput screening of metal toxicity and avoids uncertainties in metal speciation inherent to chelator buffered systems. Details are given how to prepare the resin to obtain a target metal ion activity.     

Electrocoagulation of olive mill wastewaters to enhance biogas production

Objectives

To assess the combination of electrocoagulation and anaerobic co-digestion of olive mill wastewaters (OMWW) with other substrates, such as chicken manure, in a continuous stirred tank reactor for biogas production.

Results

Anaerobic digestion of OMWW treated by electrocoagulation allowed higher production of biogas, up to 0.74 l biogas g^?1 COD introduced compared to untreated or diluted olive mill wastewaters (OMWW) (0.37 and 0.6 l biogas g^?1 COD) respectively. Pretreated OMWW co-digested with chicken manure at different volumic ratios OMWW/manure in a continuous stirred tank reactor under mesophilic conditions revealed that OMWW/manure (7:3 v/v) was optimal for biogas production and process stability.

Conclusion

Anaerobic digestion could achieve promising results in depollution and valorization of OMWW under a continuous stirred tank reactor.

     

Growth and phosphorus nutrition of rice when inorganic fertiliser application is partly replaced by straw under varying moisture availability in sandy and clay soils

Background and aims

The combined effects of (1) reduced soil moisture availability, (2) reduced application of inorganic fertilisers while incorporating straw, (3) soil type, and their effects on growth, root system plasticity, phosphorus (P) nutrition of rice, and soil P dynamics are poorly known, but very important when aiming to increase the efficiency of water and P use.

Methods

Using large pots a three-factor factorial experiment was conducted with two moisture treatments (i.e. continuous flooding, and draining of top soil after flowering while subsoil was kept moist through capillary action), three fertilisation treatments; with (P1) and without (P0) applications of inorganic P fertilisers, and 25 % of inorganic fertilisers reduced while incorporating straw (5 t ha^?1), and soil type (i.e. clay and sandy soils with 15 and 9 mg P kg^?1 soil, respectively in P0). Shoot and root growth, root system plasticity, P nutrient status and soil P dynamics were measured.

Key results

Straw incorporation with reduced inorganic fertiliser application ensured a higher shoot dry weight and yield only in flooded clay soil as compared with P0 and P1, and a similar shoot dry weight and yield to P1 under drained clay soil. A positive growth response was facilitated by an increased water-use efficiency and rate of photosynthesis in shoots, and increased root system plasticity through the production of greater root length, more roots in deep soil layers, and an increased fraction of fine roots. Straw enhanced P extractability in soil. Drained soil reduced P uptake (15–45 %) and increased P-use efficiency. In addition to the re-translocation of P from senescing leaves and stems under both moisture conditions, the P concentration in green leaves under drained condition was also reduced (41–72 %).

Conclusion

Growth benefits of straw incorporation were observed in clay soil under both moisture conditions, and this was facilitated by the improved P availability, increased P uptake, and greater root system plasticity with the production of deeper and finer roots, compared with that in sandy soil, and inorganic fertiliser applications alone. As P uptake was reduced under drained soil, P re-translocation and % P allocated to panicles increased.     

Selenium accumulation in durum wheat and spring canola as a function of amending soils with selenite, selenate and or sulphate

Aims

A comparison was performed between plant species to determine if extractable, rather than total soil Se, is more effective at predicting plant Se accumulation over a full growing season.

Methods

Durum wheat (Triticum turgidum L.) and spring canola (Brassica napus L.) were sown in potted soil amended with 0, 0.1, 1.0, or 5.0 mg kg^?1 Se as SeO₄ ^2? or SeO₃ ^2?. In addition, SeO₄ ^2?-amended soils were amended with 0 or 50 mg kg^?1 S as SO₄ ^2?. Soils were analyzed for extractable and total concentration of Se ([Se]). Twice during the growing season plants were harvested and tissue [Se] was determined.

Results

Plants exposed to SeO₃ ^2? accumulated the least Se. Fitted predictive models for whole plant accumulation based on extractable soil [Se] were similar to models based on total [Se] in soil (R²?=?0.73 or 0.74, respectively) and selenium speciation and soil [S] were important soil parameters to consider. As well, soil S amendments limited Se toxicity.

Conclusions

Soil quality guidelines (SQGs) based on extractable Se should be considered for risk assessment, particularly when Se speciation is unknown. Predictive models to estimate plant Se uptake should include soil S, a modifier of Se accumulation.     

Comparative responses of a non-N-fixing shrub and an actinorhizal N-fixing shrub to N fertilization

Background and aims

Variations in responses to soil N between a non-N-fixing shrub, Baccharis halimifolia L., and a N-fixing shrub, Morella cerifera (L.) Small, were tested over 12 weeks to determine whether N availability is the sole cause of persistent dominance of M. cerifera on barrier islands.

Methods

Plants were supplied increasing levels of soil N up to 200 mg kg^?1. Measurements included gas exchange and chlorophyll fluorescence parameters across treatments, species, and time. Tissues were analyzed for differences in biomass and nutrients.

Results

Baccharis halimifolia had reduced physiological responses across all treatment levels, but M. cerifera had comparatively few variations. Across all treatments B. halimifolia photosynthesis and stomatal conductance were reduced by 62 and 76 %, respectively,by week 12. Increasing foliar δ¹⁵N values across treatments for M. cerifera indicated a shift from utilizing fixed N to available soil N. Biomass was highest at 200 mg kg^?1 N for both species. Baccharis halimifolia showed indications of stress response and resource limitation based on physiological responses, nutrient contents, and isotope effects.

Conclusions

Baccharis halimifolia showed signs of co-limitation of both N and P whereas M. cerifera was limited by neither, suggesting that dominance of M. cerifera is only partially explained by actinorhizal symbiosis and N availability.     

Soil CO2 efflux in response to the addition of water and fertilizer in temperate semiarid grassland in northern China

Background and aims

Knowledge about the effects of water and fertilizer on soil CO₂ efflux (SCE) and Q ₁₀ is essential for understanding carbon (C) cycles and for evaluating future global C balance. A two-year field experiment was conducted to determine the effects of water, fertilizer, and temperature on SCE in semiarid grassland in northern China.

Methods

SCE, as well as environmental factors was measured in two grasslands, one with bunge needlegrass (BNE, Stipa bungeana) and one with purple alfalfa (ALF, Medicago sativa), with four treatments: CK (unwatered and unfertilized); W (50 mm water addition yr^?1); F (50 kg phosphorus (P) fertilizer ha^?1 yr^?1 for ALF, 100 kg nitrogen (N)?+?50 kg P fertilizer ha^?1 yr^?1 for BNE); and W + F.

Results

During the 11-month experimental period from July 2010 to October 2011, the addition of water consistently stimulated mean SCE in BNE and ALF, and the positive effects were relatively stronger during dry seasons. P fertilization consistently enhanced SCE in ALF, and the positive effect was strongly dependent on the availability of soil water. The effects of N plus P fertilization on SCE in BNE varied seasonally from significant increases to small reductions to no response. Water addition increased the Q ₁₀ of SCE in ALF by 11 % but had no effect in BNE. Fertilization, however, reduced the Q ₁₀ of SCE by 21 % and 13 % for BNE and ALF, respectively. Models that rely only on Q ₁₀ underestimated the emissions of soil CO₂ by 8–15 % at the study site, which was mediated by species and treatment.

Conclusions

Responses of SCE and its temperature sensitivity to water and fertilizer may vary with species and depend on the period of measurement. Models of SCE need to incorporate the availability of ecosystemic water and nutrients, as well as species, and incorporate different environmental factors when determining the impact of water, nutrients, and species on SCE.     

The critical soil P levels for crop yield, soil fertility and environmental safety in different soil types

Background and aims

Sufficient soil phosphorus (P) is important for achieving optimal crop production, but excessive soil P levels may create a risk of P losses and associated eutrophication of surface waters. The aim of this study was to determine critical soil P levels for achieving optimal crop yields and minimal P losses in common soil types and dominant cropping systems in China.

Methods

Four long-term experiment sites were selected in China. The critical level of soil Olsen-P for crop yield was determined using the linear-plateau model. The relationships between the soil total P, Olsen-P and CaCl₂-P were evaluated using two-segment linear model to determine the soil P fertility rate and leaching change-point.

Results

The critical levels of soil Olsen-P for optimal crop yield ranged from 10.9 mg kg^?1 to 21.4 mg kg^?1, above which crop yield response less to the increasing of soil Olsen-P. The P leaching change-points of Olsen-P ranged from 39.9 mg kg^?1 to 90.2 mg kg^?1, above which soil CaCl₂-P greatly increasing with increasing soil Olsen-P. Similar change-point was found between soil total P and Olsen-P. Overall, the change-point ranged from 4.6 mg kg^?1 to 71.8 mg kg^?1 among all the four sites. These change-points were highly affected by crop specie, soil type, pH and soil organic matter content.

Conclusions

The three response curves could be used to access the soil Olsen-P status for crop yield, soil P fertility rate and soil P leaching risk for a sustainable soil P management in field.     

Nitrogen deposition and soil carbon content affect nitrogen mineralization during primary succession in acid inland drift sand vegetation

Background and aims

Two inland dunes in the Netherlands receiving low (24) and high (41 kg N ha^?1 yr^?1) nitrogen (N) deposition were compared for N dynamics and microbial activity to investigate the potential effect of N on succession rate of the vegetation and loss of pioneer habitats.

Methods

Primary succession stages were sampled, including bare sand, and vegetation dominated by Polytrichum piliferum, Campylopus introflexus, lichens and grasses respectively, representing a series of vegetation types in undisturbed drift sand sites with succession starting on bare sand containing virtually no organic matter. Microbial characteristics and potential N mineralization were analysed in a laboratory experiment.

Results

Organic matter accumulated during succession, resulting in a lower pH and in higher microbial biomass (bacteria and fungi), respiration and net N mineralization. The increase in respiration and N mineralization was largely due to the development of an ectorganic layer in the middle stages of succession. The observed effects of N deposition were (1) decrease of microbial biomass, (2) higher net N mineralization per m², (3) higher levels of free nitrogen in the soil, and (4) a higher microbial N:P ratio.

Conclusions

Elevated N deposition leads to higher N availability which may cause accelerated succession.     

Successive straw biochar application as a strategy to sequester carbon and improve fertility: A pot experiment with two rice/wheat rotations in paddy soil

Aims

A pot study spanning four consecutive crop seasons was conducted to compare the effects of successive rice straw biochar/rice straw amendments on C sequestration and soil fertility in rice/wheat rotated paddy soil.

Methods

We adopted 4.5 t ha^?1, 9.0 t ha^?1 biochar and 3.75 t ha^?1 straw for each crop season with an identical dose of NPK fertilizers.

Results

We found no major losses of biochar-C over the 2-year experimental period. Obvious reductions in CH₄ emission were observed from rice seasons under the biochar application, despite the fact that the biochar brought more C into the soil than the straw. N₂O emissions with biochar were similar to the controls without additives over the 2-year experimental period. Biochar application had positive effects on crop growth, along with positive effects on nutrient (N, P, K, Ca and Mg) uptake by crop plants and the availability of soil P, K, Ca and Mg. High levels of biochar application over the course of the crop rotation suppressed NH₃ volatilization in the rice season, but stimulated it in the wheat season.

Conclusions

Converting straw to biochar followed by successive application to soil is viable for soil C sequestration, CH₄ mitigation, improvements of soil and crop productivity. Biochar soil amendment influences NH₃ volatilization differently in the flooded rice and upland wheat seasons, respectively.     

Plant phosphorus availability index in rehabilitated bauxite-processing residue sand

Background and aims

Soil phosphorus (P) indices that have been originally developed and applied to agricultural soils for predicting P uptake by plants were examined in a pot experiment to determine the most suitable index for P availability in bauxite-processing residue sand (BRS).

Methods

Pot trials with ryegrass were established using BRS that had been amended with various organic (greenwaste compost, biochar and biosolids) and inorganic (zeolite) materials and different levels of di-ammonium phosphate fertiliser. Soil P availability indices tested included anion-exchange membrane (AEM-P), 0.01 M calcium chloride (CaCl₂-P), Colwell-P, and Mehlich 3-P.

Results

AEM-P was found to most closely reflect the available P status in BRS across all treatments, and had the strongest associations with plant P uptake compared to Colwell-P, Mehlich 3-P and CaCl₂-P. AEM-P was more closely correlated with P uptake by ryegrass than other P indices, while Colwell-P was closely related to leaf dry matter. Interestingly, a strong inverse relationship between plant indices and pH in BRS growth media was observed, and an adequate level of plant P uptake was found only in 15 year-old rehabilitated BRS with pH <?8.0.

Conclusions

AEM-P was found to be the most suitable index for evaluating P availability in highly alkaline BRS and pH was an important parameter affecting uptake of P by ryegrass. Importantly, time is required (> 5 years) before improved uptake of P by plants can be observed in rehabilitated residue sand embankments.     

Seven years of repeated cattle manure addition to eroded Chinese Mollisols increase low-molecular-weight organic acids in soil solution

Background and aims

Organic amendments are an option in enhancing soil biological productivity. Limited research exists on the effects of long-term cattle manure addition on low-molecular-weight organic acids (LMWOAs) concentrations in corn (Zea mays L) and soybean (Glycine max L.) fields in the region of soil erosion. The purpose of this study was to investigate the potential influence of cattle manure on the LMWOAs concentration in erosion soil.

Methods

A field experiment was established in Hailun city, Northeast China to determine the impact of long-term cattle manure addition on the total amounts of main LMWOAs in eroded Mollisol fields. There were three levels of simulated-erosion, which removed 0, 10 and 30 cm of topsoil. Two soil amendments were: (1) chemical fertilizer at the rate normally used by farmers in the region and (2) chemical fertilizer plus 15,000 kg?ha^?1 (dry weight basis) of cattle manure. Main LMWOAs in soil were assessed at the flowering stage of soybean and the jointing stage of corn.

Principle results

Compared to chemical fertilizer alone, 7-years of repeated cattle manure addition significantly increased total amounts of main LMWOAs in rhizosphere about 9–70 times and bulk soil about 6–62 times. The magnitude of increase by cattle manure was in the order of oxalate>malate>malonate>lactate>maleate in corn plots, and oxalate>malate>malonate>lactate in soybean plots. In comparison, cattle manure and topsoil removal had larger effect on LMWOAs concentrations in corn plot than soybean plot. The addition of cattle manure application and top soil removal had significant independent influence on main LMWOAs concentration in soil solution.

Conclusion

This study suggested that addition of cattle manure would be an effective approach in modifying soil biological properties through the increases in low-molecular-weight organic acids to eroded Chinese Mollisols.     

Contrasting effects of manure and green waste biochars on the properties of an acidic ferralsol and productivity of a subtropical pasture

Background and Aim

We hypothesised that amending an acidic ferralsol with biochar would improve the productivity of a subtropical dairy pasture via reducing soil acidity related constraints and result in improved nitrogen use efficiency. We examined two contrasting biochars with different carbon, nutrient content and acid neutralising values.

Methods

Field plots were amended with one of three biochar treatments (Nil, feedlot manure biochar [FM], green waste biochar [GW]) in combination with presence or absence of NPK fertiliser and presence or absence of liming. The FM and GW biochars had a carbon content of 44 and 76 %, available phosphorous of 5,960 and 93 mg kg^?1, and liming values of 13 and 5.6 %, respectively. The pasture was managed to supply year round high quality feed for dairy production.

Results

The FM biochar increased total pasture productivity by 11 % and improved the agronomic nitrogen use efficiency by 23 %. It also reduced soil acidity but did not significantly affect the pH dependent soil cation exchange capacity. The GW biochar did not improve pasture productivity. Both biochars resulted in an increase in the soil carbon density.

Conclusions

The high available phosphorous content of FM biochar makes it an effective amendment for acidic ferralsols. Greenwaste biochar did not have sufficient acid neutralising capacity or phosphorous content to reduce soil acidity constraints. Both biochars enhance soil carbon storage in pasture systems on ferralsol.